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Investments in equity securities (Detail) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Summary of Investment Holdings [Line Items] |  |
Cost Basis | $ 83,177 | $ 75,506
Net Unrealized Gains | 200,064 | 196,082
Fair Value | 283,241 | 271,588
Banks, insurance and finance [Member] |  |
Summary of Investment Holdings [Line Items] |  |
Cost Basis | 14,966 | 15,707
Net Unrealized Gains | 82,006 | 75,936
Fair Value | 96,972 | 91,643
Consumer products [Member] |  |
Summary of Investment Holdings [Line Items] |  |
Cost Basis | 12,198 | 12,658
Net Unrealized Gains | 80,191 | 92,091
Fair Value | 92,389 | 104,749
Commercial, industrial and other [Member] |  |
Summary of Investment Holdings [Line Items] |  |
Cost Basis | 56,013 | 47,141
Net Unrealized Gains | 37,867 | 28,055
Fair Value | $ 93,880 | $ 75,196

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